Apparatuses which permit the control of a flow of articles are useful wherever there is a need for accumulating articles in a buffer area between an upstream delivery station (e.g. a container filling and capping unit) and a downstream receiving station (e.g. a container labeling and/or wrap around station) in the event of a speed rate differential between the stations, e.g. when the downstream station is either shut down or running at an insufficient speed, whereby the articles fed from the upstream delivery station can not be properly handled.
Such apparatuses, which provide the ability to set the amount of articles temporarily stored in the buffer area, are commonly referred to as “accumulators”. Depending upon the room available and the configuration of the manufacturing plant, the accumulator may be of planar/straight or spiral/helical form.
U.S. Pat. No. 6,591,963 to Wipf discloses a straight storage apparatus comprising a carriage which can be displaced along a conveying plane. A pair of deflecting rollers is arranged on the carriage to guide an endless conveying means. One of the deflecting rollers subdivides a storage strand of the apparatus in an entry-side storage strand and an exit-side storage strand. The length of the storage strand can be changed, as does the capacity of the storage apparatus.
In theory, such a solution seems satisfactory because its construction appears quite simple. In practise however, drawbacks come to light when the setting of the apparatus must be achieved and in particular when the conveyor has to be tensioned. As disclosed in U.S. Pat. No. 6,591,963, tensioning means are provided on the carriage, the deflecting rollers being mounted in a mutually resilient manner. Although the tensioning process is not specifically disclosed in the Wipf patent, the skilled person can understand that the tensioning is achieved by moving the rollers towards each other, thereby exerting a traction effort on the circular portions of the conveying means wrapped around the deflecting rollers. The reaction effort exerted on the deflecting rollers by the conveying means generate undesired though inevitable bending and shear stresses on the axis of rotation of the rollers, thereby increasing the risk of axis wear, fatigue and, possibly, rupture.
U.S. Pat. No. 6,152,291 to Steeber et al, assigned to Hartness, discloses a spiral accumulator having an infeed conveyor driven in a first direction, and an outfeed conveyor spaced apart from the infeed conveyor and driven in an opposite direction. A transport member carrying a rotatable wheel is provided between the infeed and outfeed conveyors. The rotatable wheel is engaged on both sides by the infeed and outfeed conveyors so that the wheel is caused to rotate and the transport member may be caused to move along a path parallel to the infeed and outfeed conveyors depending upon the relative speed thereof. An article transfer member is also carried by the transport member for deflecting articles from the infeed conveyor to the outfeed conveyor. Articles deflected from the infeed conveyor temporarily run on a dead plate provided around the wheel over the space between the conveyors.
The Hartness accumulator does not have the hereabove mentioned drawback of Wifp's apparatus, since the stresses resulting from the tensioning of the infeed and outfeed conveyors are not transmitted to the rotatable wheel.
However, operating the Hartness accumulator has revealed uncontrolled movements of the articles in the turnaround area above the wheel, and more specifically at the junction of the (moving) infeed conveyor and the (still) dead plate, where the conveyor tends to move the articles ahead, whereas the dead plate is forcing them to loose headway. In addition, tacky articles may stick to the (still) surface of the transfer member. Subsequent uncontrolled movements of the articles may result in article jam and failure of the whole accumulating process, thereby causing the accumulator to be stopped, along with the entire upstream part of the manufacturing plant.
In order to improve article transfer, it was later on proposed to equip the article transfer member with an endless drive belt that is disposed along the transfer path so as to contact and move articles therealong, see U.S. Pat. No. 6,698,581 to Steeber et al, assigned to Hartness.
This solution seems satisfactory prima facie, but movement of the endless drive belt has to be synchronized with the infeed and outfeed conveyors. In order to achieve such synchronization, there is provided a complex and heavy transmission mechanism including a toothed wheel engaging the infeed and outfeed conveyors.